System for coordinating connection requests

ABSTRACT

A coordination system coordinates connection requests of a modular connection system to a switching control system. The connection system controls connections at a logic level, and the switching control system controls connections at a physical level. Coordination modules have the following elements. A receiver receives and buffer-stores connection requests produced from the connection system for an active connection end point involved with a connection. A connection request, which is buffer-stored by the coordination modules, is passed on to the switching control system when the coordination modules have received control over an active connection end point. Control over a specific active connection end point is surrendered to one another such that only one coordination module has control over this specific active connection end point at a specific point in time.

BACKGROUND OF THE INVENTION

In the development of future switching systems, efforts are being madeto design software systems which are as modular as possible forcontrolling the switching system. This is being done primarily withrespect to better decoupling of the individual functions of a switchingsystem and thus of a simpler subsequent modification capability andimproved reusability of the switching software in further developments.

General considerations of the possibility of priority assignment toprocesses are known, inter alia, from the Article"Proze-Prozessor-Zuordnung in Multi prozessorsystemen mit globalen undlokalen Speicher resourcen zur Steuerung von Vermittlungsprozessen"[Process-processor assignment in multiprocessor systems having globaland local memory resources for controlling switching processes] by H.-J.Schwertfeger in the Journal Nachrichtentechnik Elektronik[Telecommunications Electronics], Vol. 35, No. 10, 1985, Berlin, pages365-370.

A general software model for an ATM switch node is known from thearticle "An ATM-Switching Test" by G. P. Balbony et. at., in thedocument European Trans actions on Telecommunications and relatedTechnologies, Vol. 2, No. 4, Aug. 1991, Milan, pages 391-401.

In modular connection systems for controlling connections at the logiclevel, it is highly conducive for the improvement of the modularizationcapability if the modules of such a connection system are able to submitautonomous connection requests to a switching control system forcontrolling the connections at the physical level. However, problems inthe coordination of the connection control result from this autonomousproduction of connection requests.

SUMMARY OF THE INVENTION

The invention is based on the problem of specifying a coordinationsystem by means of which coordination of the autonomous connectionrequests of a connection system for controlling connections at the logiclevel is achieved with respect to a switching control system forcontrolling connections at the physical level.

This problem is solved by a coordination system for coordinatingconnection requests of a modular connection system to a switchingcontrol system, the connection system being used for controllingconnections at the logic level, and the switching control system beingused to control connections at the physical level. The coordinationsystem has coordination modules which are designed such that they:

receive from the connection system and buffer-store connection requestsproduced for an active connection end point involved with theconnection;

pass on a connection request, which is buffer-stored by them, to theswitching control system when they have received control over an activeconnection end point; and

surrender control over a specific active connection end point to oneanother in such a manner that only one coordination module ever hascontrol over this active connection end point at a specific point intime.

The coordination system according to the invention results in it onlyever being possible to submit one connection request to the resourcecontrol system, of the connection requests produced by the connectionsystem, at a specific point in time. This ensures a logically sensiblesequence of connection requests to the resource control system.

In a further embodiment of the present invention the coordination systemhas:

coordination modules of a first type which are designed in such a mannerthat they can achieve control over in each case one active connectionend point of a connection;

coordination modules of a second type which are designed in such amanner that they can achieve control over in each case two activeconnection end points of a connection, there being in each case only onecoordination module of the second type per connection end point pair inthe coordination module chain of a connection; and

priority control in accordance with which a coordination module hashigher priority with respect to the control of a connection end pointthe closer it is to the end point of the coordination module chain.

a connection is divided into a plurality of connection ends, oneconnection end and thus the associated coordination modules beingbounded by an active connection end point and at least one centralcoordination module. This results in it being made possible forconnection requests for an individual active connection end point tohave to be coordinated only within one connection end, that is to sayamong the coordination modules of a single connection end. Since thecentral coordination module has the lowest priority, it cannot achievecontrol over the associated two connection ends until all thecoordination modules at these two connection ends have, for their part,released control. This results in those connection requests on the basisof which two active connection end points involved in the connection areintended to be connected and which are thus at the end of a connectioncontrol process not being able to be passed through by the centralcoordination module until all the preparatory control processes havebeen completed. This avoids such a connection request being passedthrough prematurely.

In another embodiment of the present invention a coordination module isdesigned in such a manner that it can pass on a connection request for aconnection end point over which, in principle, it cannot achieve controlto another coordination module which can achieve control over thisconnection end point. This results in a coordination module also beingable to pass a connection request through for a connection end pointover which it can itself not achieve control.

In yet a further embodiment of the present invention one and only onecoordination module is permanently assigned to teach module of theconnection system, and the communication of the coordination modulestakes place via the communications channels of the modules of theconnection system. In yet another embodiment of the present invention acoordination module is designed in such a manner that the transfer of aconnection request into a coordination module conforms with a procedurecall. This embodiments of the invention have the advantage that thedynamic complexity for the connection-related communication is inconsequence reduced.

In another embodiment of the present invention the coordination modulesare designed in such a manner that they translate the connectionrequests passed to them in each case into a connection command which iscomprehensible for the switching control system. This embodiment of theinvention has the advantage that the decoupling of the connection systemfrom the switching control system is in consequence improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel,are set forth with particularity in the appended claims. The invention,together with further objects and advantages, may best be understood byreference to the following description taken in conjunction with theaccompanying drawings, in the several Figures of which like referencenumerals identify like elements, and in which:

FIG. 1 shows the structure of an ATM switching system.

FIG. 2 shows the modular composition of the call processing system.

FIG. 3 shows the view of the segments of the connection system and ofthe coordination modules of the coordination system with respect to aconnection.

FIGS. 4 to 8 show the sequence of setting up a connection in terms oflocation.

FIGS. 9 and 10 show the sequence when a tone is applied to a stablecall.

FIGS. 11 to 15 show the sequence for setting up a three-way call in thepresence of a stable two-way call.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows the structure of an ATM switching system in which thesoftware structure according to the invention can be used to implementthe network layer.

The principles of the switching functions for setting up STM connectionsor ATM connections are comparable. Thus, for example, a virtual paththrough the relevant switching networks is also specified for an ATMconnection before the actual data transfer starts. All the cells in anATM connection are transferred via this path. In general, a plurality ofconnections will be involved in an ATM link. ATM cells which belong tothe same connection are assigned the same VCI/VPI identifier (virtualconnection/path identifier) in the cell header.

A selected path must be reserved in software lists for all links whichproduce a traffic concentration, in order to prevent an overload on theATM links.

The number of cells which are transferred in a specific time intervaldefines the bandwidth which is occupied on a link by a specific ATMconnection. The associated bandwidth is monitored in aconnection-specific manner by a user/network interface in order toprevent the switching networks being flooded in an unauthorized mannerby a specific user (policing). The said software list is controlled by asoftware resource system RHS, which is implemented in a controldirectory unit SLUC of a subscriber unit SLU.

The VCI/VPI identifier which is assigned to a specific ATM connectionand is abbreviated in FIG. 1 with the designation VCI is always validfor a specific link. Before the ATM cells are transferred onwards onanother link, a new VCI/VPI identifier is entered in the header of anATM cell (header translation HT). This header translation likewise takesplace on the user/network interface which is not illustrated.

The header translation is additionally carried out in each case beforepassing through a switching network. In this case, a routing identifierR, which describes the specified path through the following switchingnetwork, is attached to an ATM cell at the same time as the entry of anew VCI/VPI identifier. The routing identifier R is evaluated within thefollowing switching network in order to switch the cell through to thecorrect outgoing link. For a virtual path, only the VPI identifier iscalculated again in the interface circuit IFH or in the access device AU(in the case of a remote SLU), while the VCI identifier, which isassigned to the individual connections, remains unchanged. All the cellshaving the same VPI identifier thus receive the same routingidentifiers, which makes it possible for a plurality of virtualconnections to be switched in a transparent manner over the same virtualpath.

FIG. 1 shows the header translation for a virtual ATM connection via themain switching network SNB. A one-way connection from a subscriber lineunit SLUA to a subscriber line unit SLUB is illustrated as the virtualATM connection. The header translations carried out for one ATM cell aredescribed in more detail in the following text.

The first header translation HT is carried out by the subscriber moduleSLMA. In this subscriber module, the routing identifiers RA for the paththrough the local switching network ASNS of the subscriber unit SLUA areattached to the ATM cells, and the VCIA identifier is entered in theheader of the ATM cells.

The second header translation for the central switching network SNB isproduced by the broadband access device AUB. In this broadband accessdevice, all the incoming cells having the path identifier VCIA receive anew path identifier VCIB and a new routing identifier RB for the paththrough the main switching network SNB.

The third, and last, header translation is carried out in the subscriberunit SLUB at the B-end in the IFH. There, all the incoming cells havingthe path identifier VCIB receive a new path identifier VPIC, as well asnew routing identifiers RC for the path through the local switchingnetwork ASNS of the subscriber unit SLUB.

FIG. 2 shows the modular composition of a specific user system, namelythe call processing system for controlling calls and its arrangementwith respect to further software systems for controlling connectionswithin a switching system.

The call processing system comprises a call control system CCS forcontrolling a connection at the logic level, an interface system ESISfor shielding the call control system from different signaling variants,and a coordination system LSS for coordination of the logic connectionrequests, which are produced by the call control system, with respect toa switching control system PSS. The interface system ESIS and the callcontrol system can be combined as a specific connection system, namelythey can be considered as or called a call connection system. Theswitching control system can be considered as the central controller ofa resource control system.

Furthermore, a processing system ITP (system administration) and aprocessing system SIG (signaling administration) for controllingsignaling connections of a signaling system are illustrated at the samelevel as the call processing system. In the same way as the callprocessing system, these processing systems contain connection systemswhich use the switching control system PSS to implement their logicconnection wishes at the physical level.

FIG. 2 furthermore shows the decentralized part of the resource controlsystem, namely resource systems RHS for local control of the resourcesof the switching system, and the main switching network SNB which iscontrolled directly by the switching control system, as the singleresource of the switching system.

The following text describes the call processing system.

The ESIS produces the shielding of the call control system CCS fromdifferent signaling variants, by converting the different signalingschemes into a general information interface between the ESIS and CCS.The internal structure of the ESIS is strictly modular, with separatesoftware modules for every supported signaling system and every variantof it. Corresponding entities are produced or removed by these softwaremodules in conjunction with connections, depending on whichconnection-specific signaling requests occur. However, despite thedifferent software modules, the call control system CCS always sees ageneral information interface to the ESIS.

In addition, the ESIS is responsible for the connection-relatedsignaling interchange between different signaling systems.

The call control system CCS is used for controlling the connection atthe logic level. Its tasks include traffic routing, standard connectionsetting up and clearing down, handling of performance features,informing the charge system and the statistical system of call events,etc. The area of the CCS tasks does not include the control of settingup and clearing down the physical connection. This is admittedlyinitialized by the CCS, but it is controlled autonomously by theswitching control system PSS. Only those tasks of the CCS which relateto connection control are considered in more detail in the followingtext.

The CCS comprises two types of software units, namely steady-statemodules (managers) and transient modules, which are designated callsegments. The said call segments produce a series of entities (processentities or data entities) per connection, which entities communicatewith one another via a common information interface. In the followingtext, the said entities are also designated segments, and thecommunicating series of entities is also designated a call chain.

The call segments include access segments ATS which represent thetechnical features of the relevant port, user segments UTS whichrepresent the performance features of the user, associated segments ASwhich represent the association of the A-end and the B-end, and featuresegments FS which do represent non-standard features of a connection,that is to say individual features. The said call segments for aconnection are produced or removed as a function of connection-specificrequests and subscriber/network features.

The coordination system LSS coordinates connection requests whichoriginate from different call segments and ESIS segments. For thispurpose, the coordination system must buffer store the connectionrequests received from each segment. This is done in a coordinationmodule LSM, which is assigned per segment. Every time a switchingcoordination module receives a new connection request from a segment,the status of the coordination module is evaluated and updated. Adistributed control mechanism between the coordination modules ensuresthat the coordination system provides a consistent physical connectionrequest with respect to the switching control system PSS.

The switching control system is described in the following text.

The switching control system is a basic service system for all the usersystems of the switching system which request connections within theswitching system. Apart from simple connection requests, the switchingcontrol system also deals with specific connection requests for thereconfiguration of connections which have been set up for the usersystems.

The switching control system produces in each case one autonomous entityper connection request. In consequence, the interactions between theswitching control system and the resource systems and main switchingnetwork are independent of the status of the entities of the respectiveuser system.

The coordination system transforms the private view of a connection,which can be adapted to the segments (entities) of the call controlsystem and of the signaling interface system, into a single consistentconnection request with respect to the switching control system. Forthis reason, the switching control system may carry out connectionorders from the coordination system in an unconditional manner. The onlyreasons for a negative acknowledgement to the coordination system areblocking conditions of the controllers of the switching networks (forexample a negative acknowledgement from one of the resource systems RHS)or defects in the switching networks themselves (for example a negativeacknowledgement from individual switching networks).

Every connection request to the switching control system causes a newtransaction of the switching control system. Such a transactioncomprises the control of the resource systems involved and thus thecoordination of the setting up of a physical path through the switchingnetworks of the switching system.

Since the actual resource handling (path resources and service unitresources) is separated from the switching control system and is carriedout by resource systems independent of them, the switching controlsystem does not require any assignment to a specific central controlprocessor of the central control processors GPx, . . . GPy (see FIG. 1).Furthermore, there is no limitation on having to use connectionrequests, which originate from the same call chain, on the same entityof the PSS. This allows very effective implementation of the functionsof the switching control system within the hardware system. Everycentral control processor can thus operate a plurality of entities ofthe switching control system in parallel. In consequence, a user systemcan always submit its connection requests to a switching control systemof its own central control processor. Since the switching control systemwaits for confirmations of the resource systems and/or of the mainswitching network, it is possible to carry out parallel execution ofconnection requests for different connections on in each case one singlecentral control processor. For this purpose, one specificparticularizing mechanism must be made available per central controlprocessor (for example process particularizing or data particularizing).

Resources which are assigned to a connection must be stored in aconnection-specific manner for the duration of a connection in order tobe able to clear down the connection at the end. If these data werestored in the switching control system, it would have to be ofconsiderably more complex construction. For example, a PSS entity wouldin each case have to be given for the entire duration of the connection,which would necessitate an additional state/event coupling within thePSS and, furthermore, new checks for consistency of the connectionrequests between the PSS and the user systems. In order to avoid thisincreased complexity, the connection data are stored within therespective user system. For example, the connection data for the callprocessing system are stored in data fields assigned to the coordinationsystem. In order to implement this concept, a so-called "path envelope"is passed backwards and forwards between the user system and theswitching control system, which path envelope the current connectiondata (path data and other resource data) contain. While the pathenvelope for the user system is a black box, the contents of this pathenvelope are evaluated by the switching control system in order to carryout an optimum path search for the connection requests.

In summary, the switching control system thus represents an interfacebetween the call processing system and the resource systems and/or themain switching network, which interface allows the call processingsystem to submit combined connection requests, which contain a resourceoperation and switching, in a single connection request to the switchingcontrol system. In this context, the switching control system ensuresthat the combined connection request is carried out in a coordinatedmanner.

The call control system is described in more detail in the followingtext.

As already mentioned, the call control system comprises two types ofsoftware units, namely steady-state units (managers) and transient units(segments).

Steady-state managers mainly control long-life call processing entities,for example a telephone number of a subscriber or the type of a port.There is in each case one steady-state manager per entity, which forms aneutral interface between the call processing and the steady-state database. Steady-state managers thus shield the connection control from thestructure of the physical data base. In addition to the respectiveentity, they carry out functions related such as busy/idle-handlingoperations. In order to achieve efficiency in real time, steady-statemanagers are located physically close to the data controlled by them andcan thus be contained within a software capsule of the physical database. Steady-state managers furthermore identify all the activetransient segments (entities) to which they are currently making theirservices available, and supply these active transient segments, as aresponse, with data in a format which is defined for call processing.

Transient segments control short-life entities, for example a standardconnection or a performance feature. Transient segments are produced ordestroyed on the basis of user/network actions such as "going off hook"or "placing down", and carry out logic call control functions, such asoperations for making a port busy or releasing it and carrying outspecific actions for a performance feature. At the start of aconnection, the transient segments are produced and are used at theirrespectively associated steady-state managers in order to obtain thedata required by them from the data base. The transient segments storethe data received and work with these data throughout the entireduration of a connection. At the end of a connection, the transientsegments are destroyed, and the transient data controlled by them arethus also destroyed.

The individual types of steady-state manager are described in moredetail in the following text: An access manager AM represents a physicalsubscriber/network access which is independent of the signaling type andis defined by a logic access identifier. This manager identifies theresources (channels, bandwidth and terminals) associated with a specificphysical access, as well as blocking conditions and logic useridentifiers associated with this physical access. In addition, an accessmanager carries out the access-related free/busy handling operation andassigns the access resources required for this purpose (for exampleassignment of a VPI/VCI number).

Finally, an access manager must in each case define, for the transientsegments operated by it, the link to the entities required by the nexttransient segment. In the case of an A-connection end, "define a link"for the access manager means the definition of a logic user identifier.This requires either checking a logic user identifier supplied by theuser himself or determining a logic user identifier assigned to thepresent physical access (for example in the case of an analog user). Inthe case of a B-connection end, the definition of a link means, for theaccess manager, the definition of the logic signaling type identifier.This is determined on the basis of the logic access identifier and,possibly, predetermined terminals.

A user manager UM represents a subscriber (user) who is defined by alogic user identifier (for example a telephone number). This manageridentifies the limits, provided for the specific user, for the requeston the basis of resources, administrative blocking conditions andfeatures of the user. The user manager is responsible for all thestandard call processing functions which are related to the saiduser-related data. The user manager also carries out the user-relatedfree/busy handling operation and assigns request user resources.Finally, in the case of a user at the B-connection end, the user managerdefines the logic access identification which forms the link to theentities of the next transient segment (ATS segment).

A feature manager FM is required for individual features. It controlsfeature-related data which are associated with the subscriber or thegroup which has subscribed to this performance feature. The featuremanager results in the feature data being separated from the normalsubscriber data, so that an extension to or a change of the performancefeatures does not necessarily exert any influence on the standard callprocessing.

A trunk group manager TGM controls a logic trunk group. It carries outtrunk selection at the outgoing connection end and marks a channel ofthe trunk group at the incoming connection end as busy. Furthermore, itsupplies trunk-group-related data to a trunk group segment TGS.

A network routing manager NRM evaluates the received information (forexample dialed digits) with the aid of a translator, and defines asuitable connection handling operation. The NRM can control a pluralityof translators (for example POTS, CENTREX, packet etc.), which can beadded and controlled in accordance with the wishes of the customers. Theneutral interface between call segments and the network routing managershields the call segments from the specific architecture of thetranslators.

The individual types of transient segments are described in more detailin the following text. An access segment ATS represents the control ofaccess-related transactions. It produces an autonomous request on thebasis of access resources, for example from each SETUP information item.Access resources may comprise an individual B-channel or D-channel of asubscriber, an individual connection line (trunk) or an associatedbandwidth having a plurality of channels. The ATS additionally controlsthe triggering of appropriate feature segments FS for controllingaccess-related features.

A user segment UTS represents the control of user-related transactions.In this case, it in each case produces an individual request inaccordance with user resources. The UTS additionally controls thetriggering of user features.

A trunk group segment TGS controls the involvement of a trunk of a trunkgroup in a connection. The TGS segment in this case requires that theTGM manager carry out the selection of a trunk at the outgoingconnection end, and informs it that the trunk at the incoming connectionend is busy.

An associated segment AS associates a connection pair at the A-end andB-end. At the same time, it coordinates the setting up and clearing downof a connection and initiates the translation/routing activities by theNRM manager.

A feature segment FS controls the handling of subscriber-specificperformance features. FS segments are inserted into an already existingcall chain, if they are requested by a subscriber or by the network.Every FS segment contains feature-related logic and has access tofeature-related data in the data base. The feature-related logic is thuscentralized, by the FS segment, in a single software unit. Advancedintelligent network services are supported, for example, by an FSsegment in that it forms an interface to a service control point (SCP).In principle, an FS segment can be inserted into the call chain betweenan ESIS segment and an ATS segment, an ATS segment and a UTS segment, ora UTS segment and an AS segment. This depends on factors such as therelevant trigger point and resource-related requests.

The sequence during the setting up of a connection for a standard callis described in the following text. The subscriber line module of asubscriber A initially detects a busy information item and then sends aSETUP information item to the group processor GP associated with it, atwhich point an ESIS segment is produced in order to receive thisinformation item. The ESIS segment converts the received SETUPinformation item into a general SETUP information item for the callcontrol system, requests an ATS segment and passes the general SETUPinformation item to the ATS.

The access segment ATS then requests access-related data from its accessmanager AM. The AM reads access-related data from the access data base,carries out an access-related busy/free handling operation, and,finally, passes the requested access-related data to the ATS. The ATSstores the access-related data, requests a UTS, and passes the SETUPinformation item to the UTS produced.

The UTS requests user-related data from its UM manager. The UM reads therequested data from the user data base, carries out a user-relatedbusy/free operation, and passes the requested user-related data to theUTS. The UTS then requests an AS which, for its part, in turn requestsdialed digits. The request for dialed digits is sent via an informationitem which the call chain [lacuna] from the AS inter alia to the ESIS atthe A-end. At this point in time, the call chain at the A-end comprisesESIS-ATS-UTS-AS.

The ESIS now uses the type of signaling system to determine whether adialing tone or a code receiver is required, and informs the switchingcontrol system PSS via the coordination system LSS. The PSS defines theoptimum resource configuration and then requests an assignment andconnection of the selected resources by the corresponding resourcesystem RHS. The RHS stores the selection of physical resources and thencontrols the switching through of the selected resources. When the codereceiver receives dialed digits, it sends them directly to theassociated ESIS. The ESIS then produces a request to the coordinationsystem LSS for the dialing tone to be turned off, converts the dialeddigits to a standard representation, and the call chain then sends themto the AS segment.

The dialed digits in this case flow via the ATS segment and the UTSsegment and are finally received by the AS segment. The AS sends thedialed digits to the NRM manager, which allows the dialed digits to besubjected to the necessary translation by the translator. As soon as thetranslation result is fixed, the NRM manager passes the result back tothe AS segment, which then causes a UTS segment to be produced at theB-end.

Once the end of the dialing process has been identified, the ESISsegment at the A-end causes the code receiver to be switched off bymeans of a corresponding request to the switching control system PSS viathe coordination system LSS. The switching control system PSS thencommands the resource system RHS, which turns off and releases the saidphysical resource, namely the code receiver, again.

The UTS segment at the B-end now requests data from its user manager UM,which then checks the busy counter of the telephone number, andincrements it. The UTS segment at the B-end then requests an ATSsegment. The ATS segment then requests data from its access manager AM,which then checks the access-related busy/free status, and makes theaccess busy.

The ATS segment then requests an ESIS segment, which then passes theorder to make it busy to the subscriber line module of the subscriber B,and sends the data required for this purpose. The subscriber line modulethen applies the calling current. The ESIS segment at the B-end nowrequests that the ringing tone be switched on by the coordination systemLSS, which then emits an appropriate request to the switching controlsystem PSS. The PSS determines the physical path through the switchingnetworks affected by the call, and then requests the resource system RHSto assign and switch through the ringing tone.

The physical path in the rearward directions switched through at thispoint in time. The ringing tone at the A-subscriber end is thus suppliedvia the subscriber line module SLMB.

When the B-subscriber goes off hook, this is identified by thesubscriber line module assigned to him. The subscriber line module thenturns the dialing current off and sends an OFF-HOOK information item tothe ESIS segment of the group processor GP assigned to it.

The ESIS segment then requests that the ringing tone be turned off,passes a CONNECT information item on through the call chain to the ASsegment and in consequence causes the voice path to be set up in theforward direction. Communication via the voice paths can now take place.

The coordination system LSS according to FIG. 2 is described in moredetail in the following text.

As already mentioned, the coordination system coordinates connectionrequests which originate from different segments. For this purpose, itstores the connection requests received from the different segments. Ineach case one coordination module LSM is provided for the storage of aconnection request of one segment. Every time a new connection requestis received from a segment, the status of these coordination modules isevaluated and updated. The control mechanism between the coordinationmodules ensures that the coordination system LSS always transfers asingle, consistent switching command to the switching control systemPSS.

In order to reduce any dynamic additional complexity for thecommunications requirement of the coordination system (internallybetween the coordination modules and externally between the coordinationmodules and the segments), the coordination system is strongly linked tothe ESIS/CCS system. A coordination module is preferably in each caselinked to a segment so firmly that connection requests from the segmentsto the coordination system or to the coordination modules representlocal procedure calls.

Furthermore, the information between the segments is used in order totransmit coordination information between the coordination modules. Thisis worthwhile particularly when setting up a connection. Specifically,the setting up of a connection is particularly communications-intensivefor the coordination system, since the receiver and tones must be turnedon and off. Since the information flow between the coordination modulesactually runs in parallel with the information flow of the segments, noadditional increased complexity with respect to the communication of thecall processing system is incurred if information between thecoordination modules is embedded in information for communicationbetween the segments.

Although the coordination system is thus very strongly linked to theESIS/CCS system, a clear distinction nevertheless remains between thecoordination system and the ESIS/CCS system, namely a well-definedprocedure interface.

Apart from coordination of the connection requests of segments, thecoordination system is also used for translating the connection requestsinto switching commands for the switching control system. The segmentscan thus be limited to a very abstract description in the formulation oftheir connection requests (abstract view of a connection), which regardsthe entire switching network as a black box.

The view of the segments and the coordination modules with respect to aconnection is explained in more detail in the following text, withreference to FIG. 3.

Most segments have two links, namely link-X and link-Y. Segments forspecial performance features may, however, also have more than twolinks, for example the segment for implementing three-way calling hasthree directly adjacent segments in the call chain and thus three links.The segments in each case associate a specific connection end with eachof their links. This association is defined by appropriate assignment inthe production of the segment. According to this view, a segment alwaysformulates a connection request with the aid of its logic links, forexample "connect link-X to link-Y" or "connect link-X to anannouncement".

A coordination module LSM which is permanently assigned to a specificsegment has the same data fields as the associated segment for bufferstorage of a connection request. A coordination module thus identifiesthe same links as its associated segment. In contrast to the segment,these links are, however, associated with the port address in the viewof a coordination module.

For an ATM switching network, the connection end point assigned to asubscriber or to a connecting line means a VCI/VPI number. As alreadymentioned, for a coordination module, the connection end point means aVPI/VCI number at a specific port. The port address (including the busyVPI/VCI number) of a connection end point of the call chain iscontrolled by the access manager AM and is passed via the call chain tothe appropriate coordination modules whenever an outgoing request froman active connection end point is identified.

For simplicity, a connection end point is designated a "port" in thefollowing text, without having to mention the associated VPI/VCI numberexplicitly.

The view of a connection (connection view) of a coordination modulecomprises, in addition to the port address and the VPI/VCI number, thetype of port affected as well (in this case, port can be understood tobe in the sense of a connection end point). If a resource (passive port)is intended to be connected to a specific link, the type of resource isalso indicated (for example announcement, broadcast tone, jumper) by theconnection request of a segment. The actions of the coordination systemfor a received connection request from a specific segment depend on theconnection status and the associated port types. The said status is inthis case formed by the totality of the statuses stored in thecoordination modules. Communication between the coordination modules istherefore possibly required in order to carry out a connection request.Examples of port types are: "active port" for ports which are assignedto a subscriber or to a connecting line, "announcement port", "jumperport", and "0 port" for no connections.

The internal control mechanism of the coordination system is describedin the following text.

Stimulation signals from active ports which are associated withsubscribers or connecting lines must be coordinated. For a standardcall, there are two and only two active ports which are assigned to theA-end and B-end of the standard connection. In order to coordinate astimulation signal from an active port, or to put it more precisely theconnection request derived therefrom, a control mechanism is used.According to this control mechanism, the control over an active port isalways assigned at a specific point in time to one and only onecoordination module of the coordination system. If a coordination modulehas the said control over a port, it can send connection requests forthis port to the switching control system PSS.

If a segment submits a connection request for a port over which itscoordination module assigned to it has no control at this point in time,there are three alternatives: 1st alternative: the coordination moduleis authorized to request control over the port (connection end point)from another coordination module, 2nd alternative: the coordinationmodule must wait until another coordination module releases control overthe port, 3rd alternative: the coordination module is authorized totransfer the request to another coordination module which can achievecontrol over the port.

The selection of one of the said alternatives is carried out inaccordance with priority rules which correspond with the priority rulesfor the segments of the ESIS/CCS system. In the case of the ESIS/CCSsystem, segments which are located closer to the signaling source(active port) have priority for signals which originate at theirconnection end. In an analogous manner to this, in the case of thecoordination system LSS, those coordination modules which are locatedclosest to the signaling source within the call chain have the highestpriority for control of the active port at their connection end. Thismeans that connection requests from segments which are located furtheraway and are thus prioritized lower are made subordinate to those whichare located closer to the active port. Connection requests which havebeen made subordinate are stored in the coordination module of therequesting segment, and become active as soon as the segment prioritizedhigher releases control over the active port.

In the case of the call control system CCS, the AS segment plays acentral role as a linking element between segments at the A-end and theB-end. This central role is also maintained for the AS coordinationmodule. The AS coordination module is the only coordination module whichcan achieve control over the port at the A-end and at the B-end. All theother coordination modules can achieve control only over the portlocated at their connection end.

Since the AS coordination module is the only coordination module whichcan simultaneously achieve control over the A-end and over the B-end, itis also the only coordination module which can transfer a switchingcommand to the switching control system PSS which producesthrough-switching between the A-end and the B-end.

As a result of the central role of the AS coordination module, itbecomes possible to limit the communication between the coordinationmodules to half of the call chain, the coordination of the two halvesbeing managed by the AS coordination module. While a normal coordinationmodule can never achieve control over an active port which is located onthe other side of the AS coordination module, the segment which isassociated with this coordination module can nevertheless send aconnection request to the remote connection end. These remote connectionrequests must be transferred to the AS coordination module which canfinally pass on the respective connection request to the switchingcontrol system as soon as it has achieved control over the portsinvolved.

The said priority rules apply in a, corresponding manner to a port of aremote connection end. A coordination module which is located closest tothe remote connection end point is prioritized above the coordinationmodules located more remotely from the connection end point.

The explained control mechanism for connection requests to thecoordination system is implemented by means of the internal structure ofthe data and the logic of the coordination system. In order to achieveeffective coordination within the coordination system, the statusinformation items contained in a coordination module, apart from theprivate connection data, also comprise information on the location inthe call chain which currently has control over an involved connectionend point. This information is updated whenever the said control istransferred to another coordination module. Connection requests to acoordination module originate either from a segment or from anothercoordination module.

Various connection control processes are explained in more detail in thefollowing text, with reference to FIGS. 4 to 15.

In the said figures, horizontal arrows mean the flow of informationbetween segments of the ESIS/CCS system, this information alsocontaining information on the information interchange between thecoordination modules LSM of the coordination system LSS. Vertical arrowsmean the flow of information between the call control system CCS and thecoordination system LSS. Vertical arrows which are drawn with doublelines mean either the flow of information between the coordinationsystem LSS and the switching control system PSS, or that between theswitching control system PSS and the resource system RHS or the mainswitching network SNB. The procedure interface between the ESIS/CCSsystem and the coordination system LSS is not illustrated for all theinformation flows. Information between the switching control system PSSand the main switching network SNB is illustrated only in FIGS. 6 and 8.

The illustrated information flows comprise data which change the currentstatus and/or the data fields of a coordination module LSM. Of the datafields of the coordination modules, the ct fields and cp fields areespecially worthy of mention, in which information relating to each linkof a coordination module LSM is stored, and which are described in moredetail in the following text.

The contents of act field describe which resource or which link a linkbeing considered is connected to or, to put it more precisely, isintended to be connected to. Thus, the latest connection request of aESIS/CCS segment relating to each link of the segment is stored in thect field. Since the ct fields reproduce the individual view of a segmentwith respect to the associated connection, they are also lodged by thissegment and may never be changed by the communication between thecoordination modules LSM. Valid types of ct fields are, for example,"link" (that is to say the connection is implemented from the view ofthe segments), "announcement/tone/jumper" (that is to say the segmenthas requested the connection of an announcement, a tone or a jumper tothe corresponding link), or zero (that is to say the connection or thelink has been cleared down again from the view of the segment).

The cp fields indicate the "connection end point" (CONNECTION END POINT)of a link under consideration. They contain the information on the portaddress of the physical entity which is associated with the link underconsideration. For this reason, cp fields may be changed only on thebasis of information between the coordination modules which pass on thecontrol of an active port, and never on the basis of connection requestsfrom segments. Valid information types for cp fields are "active port"(that is to say the coordination module has control, or the control iscloser to the AS coordination module) or "announcement/tone/jumper/zero"(that is to say a coordination module which is located closer to theactive port has achieved control again).

The cp fields are provided only for those coordination modules (to putit more precisely for those links of a coordination module) which canachieve control over the active port (active connection point)associated with the link under consideration, that is to say which canobtain the authorization to emit a switching command with respect to theactive port controlled by them. For this reason, all the coordinationmodules at the A-end have only one cp field, namely for that link whichleads to the port at the A-end. Analogous conditions apply in anappropriate manner to the coordination modules and links at the B-end.Thus, as the only coordination module, the coordination module AS hastwo cp fields since it can achieve simultaneous control over two "activeports" (that is to say can emit a switching command to connect two"active ports" to the switching control system PSS).

The already described priority rules are used to update the cp fields.The control over an active port is in this case passed on by a "CHANGECONTROL" information item within the coordination system. Thisinformation item may contain the information "active port" (that is tosay the control is offered to the next coordination module), "zero"(that is to say the control is passed back from a coordination modulewhich is prioritized lower) or the information on a resource"announcement/tone/jumper" (that is to say the control is passed backfrom a coordination module which is prioritized lower, and the saidresource is intended to be switched through to the opposite activeport).

In the following figures which are to be explained, separateforwards/backwards switching is considered for the connection ofreceivers etc. In order that independent through-switching of theforwards direction and rearwards direction of a connection can beensured, the control mechanism of the coordination system is alsoimplemented independently for both connection directions. For thisreason, separate cp/ct fields for the forwards and rearwards directionare provided for each link. In the information flows which areillustrated by the arrows, this is indicated by an index U or D for thecp/ct fields. While the index U represents the "upward to the remoteport" direction, the index D represents the "downward to the port atthis end" direction.

In the said figures it can clearly be identified that there is a changein the connection direction in the segment AS. This situation isexplained because the segment AS represents the center of the callchain, and the connection direction having the index U on one half ofthe call chain corresponds to the connection direction having the indexD on the other half of the call chain.

The logic connection requests contained in the cp/ct fields representthe status of the connection when all the information illustrated in therespective FIG has been processed. For the connection status illustratedin one FIG in each case, the path envelope is furthermore indicatedunderneath the information flows, which path envelope is passed backfrom the switching control system to the coordination system afterexecuting a switching command. A list of brief explanations ofdesignations which are used in the following figures now follows:

cpU=Connection end point upward

cpD=Connection end point downward

ctU=Connected to upward

ctD=Connected to downward

A=Subscriber at the A-end

B=Subscriber at the B-end

DT=Dialing tone

DF=DTMF receiver

RT=Ringing tone to the A-end

TN=Tone

lk=Link of the call chain

chA=VCI/VPI number on the SLUA link

chB=VCI/VPI number on the SLUB link

RHS=Resource system

SLU=Subscriber line unit

alloc=Allocation

con=Connection

transres=Translation result from the NRM/manager

prov=Provide

The setting up of a standard connection is now considered once againwith reference to FIGS. 4 to 8 and, in this case, especially theinvolvement of the coordination system LSS.

FIG. 4 shows the information flows after reception of the stimulationinformation item "off hook" as well as the status of the connectionbefore receipt of the dialed digits. If the calling subscriber is anISDN subscriber, then the allocation of a B-channel is initiallyproduced by the access manager AM. In consequence, the segment ATS isthe first segment in the call chain which receives the port address ofthe A-end. This port address is then passed back (in the informationitem "set up acknowledgement") to the segment ESIS, together with thedata which relate to the signaling type of the present access. Thecoordination module of the segment ESIS can then store the passed-backport address in its cp field. By means of the port address, the ESIScoordination module has at the same time received control over theconnection end point at the A-end (initialization of control).

The signaling type, which is present in FIG. 4, of the subscriber Arequires that the dialing tone DT and the DTMF receiver be turned on.For this reason, a combined allocation/connection request is transferredto the switching control system PSS. The switching control systemidentifies that the resources DT and DTMF are available in thesubscriber line unit SLUA of the subscriber A, and orders the controllerSLUC of the said subscriber line unit to switch such that the saidresources are turned on in an appropriate manner via the internalswitching network ASNS.

It can be seen from FIG. 4 that the setting up of a connection from theview of the segment ATS is already completed before receipt of thedialed digits, since the ct fields of this segment are already busy forboth connection directions. Further information on call processing,which likewise relates to the control of the setting up of a connection,is thus passed on by this segment without being influenced.

FIG. 5 shows the receipt of the dialed digits and the status of theconnection before receipt of the translation result. The dialing tone isturned off on receipt of the dialed digits. Within the call controlinformation item "digits", the coordination system information item"change control" for the coordination modules is at the same time passedon, by means of which the control over the connection end point at theA-end is passed on as far as the AS coordination module.

FIG. 6 shows the situation after receipt of the translation result, aswell as the status of the connection at the B-end before the "end ofdial" information item has been produced. After receipt of thetranslation result from the NRM manager, the port at the B-end islogically made busy by the access manager. The port address which isrequired for making it busy must therefore be passed together with the"access seize" information item down the call chain as far as thesegment ESIS. The coordination module of the segment ESIS will at thispoint initialize its cp fields with this port address.

The illustration in FIG. 4 is based on the assumption that the ringingtone is applied via the subscriber line unit SLUB of the B-subscriberfor the purpose of synchronization of bell signals and the ringing tone.This means that the ringing tone is switched through via the SLUB of theB-subscriber to the subscriber at the A-end, in a unidirectional manner.As soon as the coordination module of the segment ESIS receives the"access seize" information item, it commands the switching controlsystem to switch through the ringing tone to the subscriber line unit(line card) of the B-subscriber and transfers, embedded in the "accept"information item, the "change control" information item to the callcontrol system, up the call chain, as far as the AS coordination module.The coordination modules up as far as the AS coordination module writethe port address of the B-subscriber in their cp fields while "changecontrol" is being passed on.

Since the AS coordination module now has control over the two activeports A and B in the rearwards connection direction, it can now causethe connection to be switched through in the rearwards direction, bymeans of an appropriate command to the switching control system PSS.

If the A-end and the B-end belong to different subscriber line units,the switching control system PSS must [lacuna] the through-switching ofthe connection via three switching networks, namely the switchingnetwork ASNS of the subscriber line unit SLUB, the switching networkASNS of the subscriber line unit SLUB and the main switching networkSNB. The switching control system executes the command in that itinitially requests the controllers SLUCA and SLUCB of the appropriatesubscriber line units to network the links to the main switching deviceSNB. If the two said controllers have reported the dialed links andVCI/VPI numbers for the main switching network SNB to the switchingcontrol system, the switching control system can bring about theconnection of the links via the main switching network SNB.

As long as the subscriber connection end of the B-subscriber is notactivated, no bell signal is produced, since, until this point in time,the B-subscriber could always still go off hook in order to initiateanother call. It must be possible for the call processing to handle eventhis extremely rare case. The bell signal and the ringing tone aretherefore not applied in synchronism with one another until the "set upcomplete" information item has been received at the B-end. After thispoint in time, going off hook is interpreted as a response.

FIG. 7 shows the status of the connection at the A-end after receipt ofthe "end of dial" information item and before the B-subscriber has goneoff hook. When the segment ESIS at the A-end receives the "end of dial"information item, it causes the DTMF receiver to be turned off. The"change control" information item for updating the cp fields of thecoordination modules at the A-end is then passed up the call chain tothe AS coordination module, once again embedded in a call processinginformation item, namely in the "set up complete" information item.

FIG. 8 shows the status of the connection at the B-end on completion ofthe setting up of the connection, as well as the previous sequence, withreference to the information flows. As soon as the ESIS coordinationmodule at the B-end receives the "off hook" signaling information item,it causes the ringing tone to be switched off. In addition, it sends the"change control" information item up the call chain (embedded in the"connect" call processing information item) in order to update the othercoordination modules at the B-end. Finally, after receiving control, theAS coordination module causes the forwards connection direction to beswitched through from A to B.

The method of operation of the coordination system is explained in moredetail in the following text, with reference to further examples whichare illustrated in FIGS. 9 to 15.

FIG. 9 shows the application of a tone to a stable call. In thisexample, a feature segment FS1 breaks into the call chain at the A-endduring a stable call. The coordination module which is associated withthe feature segment FS1 is then initialized in accordance with theinstantaneous connection status. On the basis of the initialization, theFS1 coordination module identifies that the control over the active portat its connection end is instantaneously with the AS coordinationmodule. Since the FS1 coordination module has priority over the AScoordination module, it can move the control over the active port backtherefrom. This is necessary, for example, if the FS1 coordinationmodule wishes to apply a tone at the A-end. In this case, it sends arequest, which is embedded in a "change control" information item, toreceive control over the A-end up the call chain to the AS coordinationmodule. The AS coordination module then interrupts the connectionbetween A and B and passes control over the A-end to the FS1coordination module. Since the said request to receive control passesthrough every coordination module located between the FS1 coordinationmodule and the AS coordination module, all these coordination modulesidentify that the control over the A-port has now changed to the otherconnection end as seen by them. As soon as the FS1 coordination modulehas received control over the A-port, it can submit a connection requestto the switching control system PSS in order thus to produce theconnection between port A and the tone.

FIG. 10 shows the application of a tone to the remote connection end,namely the B-end in this case. In an analogous manner to the sequenceaccording to FIG. 9, the request to receive control is also passed onhere, originating from the FS1 coordination module, to the AScoordination module, which has control over the A-end and the B-end. Atthe same time as the request to receive control, the connection requestsubmitted to the FS1 coordination module is additionally passed onto theAS coordination module, since the FS1 coordination module cannot achievecontrol over the B-end. The AS coordination module implements theconnection request by means of an appropriate command to the switchingcontrol system. Control over the port A is passed back to the featuresegment FS1 in the "acknowledge" acknowledgement message to the featuresegment FS1. FIG. 10 shows the situation after all the coordinationinformation has been interchanged: FS1 has control over the port A,while the connection between the B-end and the tone is implemented inthe AS coordination module (that is to say only the AS coordinationmodule has a path envelope!). As soon as the FS1 segment ends theconnection request with respect to the application of the tone, theassociated FS1 coordination module dispenses with control over theA-end. In consequence, the AS coordination module receives control overthe A-end back, and the original connection between A and B is producedagain.

As has already been illustrated a plurality of times with respect toFIGS. 4 to 10, the switching control system in each case produces a pathenvelope in order to carry out a connection request, and transfers thispath envelope to the coordination system after executing the connectionrequest. For its part, the coordination system now passes the pathenvelope which has been produced back to the switching control systemfor every new connection control process again, for example for everyrequest to clear down a connection, to interrupt a connection or toreconfigure a connection. In these said cases, the switching controlsystem evaluates the path envelope once again, in order to execute oneof the said connection requests. In order to ensure flexible pathhandling for the said connection requests, especially the complexconnection request for reconfiguration of a connection, the switchingcontrol system makes two functions available to the coordination system,namely a release function and a disconnect function, which are initiatedby the "release" and "disconnect" requests respectively. On the basis ofthe release request by means of which the path envelope issimultaneously transferred to the switching control system, the completepath is cleared down. The switching control system in this case commandsthe resource system RHS to release all the resources associated with theconnection and to clear down local paths. The switching control systemfurthermore also causes the paths via the main switching network to becleared down, in that it sends appropriate commands to the modules ofthe main switching network, which produce the header translation.

On the basis of the disconnect request, by means of which the pathenvelope to the switching control system is likewise simultaneouslytransferred, the path chain is only slightly changed. The connection isinterrupted at one end of the path affected by the disconnect request,while the other end of the path remains in the path chain of the pathenvelope. The path envelope passed back to the coordination systemcontains the new path configuration (see FIG. 9).

The coordination system selects the suitable request on the basis of itsinternal data. For example, the coordination system uses a releaserequest to end a call. In the case of reconfigurations, for example if afeature coordination module requests control over an active port, inorder to provide an announcement (see FIG. 9 and FIG. 10), the mostsensible response is to submit a disconnect request to the switchingcontrol system, since the old connection status will undoubtedly beproduced again as soon as the announcement has been completed.

In the case of a disconnect request, the coordination system mustadditionally indicate the interruption point. The interruption point isin this case selected such that it changes the existing configuration aslittle as possible. For this reason, the interruption point is as far aspossible always located at that connection end over whose active portthe associated feature coordination module requests control. If, forexample, a feature coordination module at the A-connection end requestscontrol over its corresponding A-port, it is relatively probable thatthe requested resource is likewise available on the subscriber unit atthe A-connection end. The first preference for allocation of a resourceis therefore always the subscriber unit at the near end, while a centralcontrol processor GP which has jurisdiction is used as the secondpreference.

An example of a remaining path chain, which is stored in the pathenvelope for the AS coordination module after executing a disconnectrequest from the A-connection end, is illustrated in FIG. 9.

For the implementation of the disconnect function, only the requestedactive port is passed on via the coordination module chain of thecoordination system (that is to say no data which relate to theassociated path chain are passed on among the coordination modules ofthe coordination system). A simple solution for handling the pathenvelope within the coordination system results from this. According tothis solution, one and only one path envelope is always permanentlyassigned to one coordination module. The path envelope contains pathsegments which were assigned to the connection by the switching controlsystem in response to a connection request.

In order to avoid resources hanging in the air (path resources withoutany assignment to an active port), path segments must always beassociated with at least one active port. Therefore, whenever acoordination module releases control over an active port, thiscoordination module must ensure that all the path elements associatedwith this port are cleared down by an appropriate request to theswitching control system. If the coordination system emits a disconnectrequest relating to a passive port, that is to say a port which isassigned to a resource, it is necessary to ensure that the associatedresource is released by the switching control system again.

Since every segment has its own private view of a call, it is possiblefor a plurality of feature segments to request the application of aplurality of tones at the same time. In this case, essentially twodifferent cases can occur, namely a first case in which two featuresegments submit connection requests with respect to the same port, and asecond case in which two feature segments submit connection requests tothe coordination system relating to different ports.

In the first case, that feature segment which is located closest to theport under consideration is always carried out. This means that the tonerequested by this feature segment is physically applied as the first.The other feature segment must wait until the feature segment havingpriority releases control over the port. As soon as the feature segmenthaving priority releases control, the other feature segment canimplement its private view of the call.

In the second case, in which two feature segments wish to apply tones todifferent ports, no competition situation occurs. These tones can thusbe physically applied and switched through at the same time. This iseven possible in the case of tones which must be switched through toremote ports, since the two connection directions are switched throughindependently of one another.

A more complex example of a call, namely a three-way call, is explainedin more detail in the following text, with reference to FIGS. 11, 12,13, 14 and 15.

FIG. 11 shows an existing stable call, in the case of which theA-connection end initiates a three-way call. In this case, a tone isapplied to the B-end, and control over the A-end is passed on to athree-way segment TWC.

In order to make it possible to dial a new number from the A-end, adialing tone DT and an appropriate dialing tone receiver are switchedthrough by the ESIS segment to the port at the A-end. For this purpose,control over the port at the A-end has been transferred to the ESIScoordination module. This situation corresponds to the illustration inFIG. 12, in which two tones, namely a holding tone for the B-end and adialing tone for the A-end, are physically switched through.

As soon as the first digit is received, the dialing tone can be turnedoff. The ESIS coordination module thus releases control over the port Ain the rearward direction. The control over the port A (rearwarddirection) is passed onto the AS coordination module of the connection"A-C", since the branching position of the TWC coordination module isset to the connection "A-C". FIG. 13 shows the situation afterinterchanging all the appropriate information of the coordinationsystem.

FIG. 14 shows the connection which is set up between the A-end and theC-end. At this point in time, control over the ports A and C is locatedin the AS coordination module of the connection "A-C".

FIG. 15 shows the final status of the three-way call, in which all theconnection ends involved are connected to a jumper. While the connectionrequests of the initiating connection end (A-end) are passed on by theTWC coordination module to the switching control system PSS, theconnection requests for the other connection ends (B-end and C-end) arepassed on by the appropriate AS coordination modules to the switchingcontrol system. This situation is sketched in FIG. 15 by the variouspath envelopes which are passed back to the respective coordinationmodule from the switching control system. In the case of the example inFIG. 15, it is assumed that the jumper is available on the subscriberline unit SLUA at the A-end.

In the final status of the three-way call, the control over the port Ais located in the TWC coordination module. The control over the ports Band C is located in the respective AS coordination modules.

The invention is not limited to the particular details of the apparatusdepicted and other modifications and applications are contemplated.Certain other changes may be made in the above described apparatuswithout departing from the true spirit and scope of the invention hereininvolved. It is intended, therefore, that the subject matter in theabove depiction shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. A coordination system for coordinating connectionrequests of a modular connection system to a switching control system,the connection system controlling connections at a logic level, and theswitching control system controlling connections at a physical level,the coordination system comprising: coordination modules having:a) meansfor receiving and buffer-storing connection requests produced from theconnection system for an active connection end point involved with aconnection, b) means for passing on a connection requests, which isbuffer-stored by the coordination modules, to the switching controlsystem when the coordination modules have received control over anactive connection end point, and c) means for surrendering control overa specific active connection end point to one another such that only onecoordination module has control over this specific active connection endpoint at a specific point in time.
 2. The coordination system as claimedin claim 1, wherein the coordination system further comprises a controlsurrendering mechanism between the coordination modules, the controlsurrendering mechanism providing thata) a coordination module having alower priority must wait until control has been passed to it by acoordination module having higher priority, while b) a coordinationmodule having higher priority can request control from a coordinationmodule of lower priority.
 3. The coordination system as claimed in claim1, wherein the coordination system further comprises:a) coordinationmodules of a first type which achieve control over in each case oneactive connection end point of a connection, b) coordination modules ofa second type which achieve control over in each case two activeconnection end points of a connection, there being in each case only onecoordination module of the second type per connection end point pair ina coordination module chain of a connection, and c) priority control inaccordance with which a respective coordination module has higherpriority with respect to control of a connection end point the closerthe respective coordination module is to the end point in thecoordination module chain.
 4. The coordination system as claimed inclaim 2, wherein a respective coordination module is able to pass on aconnection request for a connection end point over which, in principle,the respective coordination module cannot achieve control to anothercoordination module which can achieve control over this connection endpoint.
 5. The coordination system as claimed in claim 1, wherein theconnection system has a plurality of modules, and whereina) only onecoordination module is permanently assigned to each module of theplurality of modules in the connection system, and b) communication ofthe coordination modules takes place via communications channels of themodules of the plurality of modules in the connection system.
 6. Thecoordination system as claimed in claim 1, wherein a transfer of aconnection request into a coordination module conforms with a procedurecall.
 7. The coordination system as claimed in claim 1, wherein thecoordination modules translate the connection requests passed to them ineach case into a connection command which is comprehensible for theswitching control system.